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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2014 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: DefaultStorageIdGenerator.html 602 2015-01-05 18:49:18Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.jsimpledb;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.lang.reflect.Method;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.nio.charset.Charset;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.security.MessageDigest;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.security.NoSuchAlgorithmException;<a name="line.13"></a>
<span class="sourceLineNo">014</span><a name="line.14"></a>
<span class="sourceLineNo">015</span>import org.jsimpledb.core.ListField;<a name="line.15"></a>
<span class="sourceLineNo">016</span>import org.jsimpledb.core.MapField;<a name="line.16"></a>
<span class="sourceLineNo">017</span>import org.jsimpledb.core.SetField;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>/**<a name="line.19"></a>
<span class="sourceLineNo">020</span> * Default {@link StorageIdGenerator} implementation.<a name="line.20"></a>
<span class="sourceLineNo">021</span> *<a name="line.21"></a>
<span class="sourceLineNo">022</span> * &lt;p&gt;<a name="line.22"></a>
<span class="sourceLineNo">023</span> * This class hashes the names into storage ID's in the range {@value #MIN_STORAGE_ID} (inclusive) to<a name="line.23"></a>
<span class="sourceLineNo">024</span> * {@value #MAX_STORAGE_ID} (exclusive); this corresponds to the range of values that are encoded in three bytes.<a name="line.24"></a>
<span class="sourceLineNo">025</span> * This provides a target space of 65,280 possible storage IDs, so collisions should be extremely rare.<a name="line.25"></a>
<span class="sourceLineNo">026</span> * &lt;/p&gt;<a name="line.26"></a>
<span class="sourceLineNo">027</span> */<a name="line.27"></a>
<span class="sourceLineNo">028</span>public class DefaultStorageIdGenerator implements StorageIdGenerator {<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>    public static final int MIN_STORAGE_ID = 0x1fb;             // first value requiring three bytes<a name="line.30"></a>
<span class="sourceLineNo">031</span>    public static final int MAX_STORAGE_ID = 0x100fb;           // first value requiring four bytes<a name="line.31"></a>
<span class="sourceLineNo">032</span><a name="line.32"></a>
<span class="sourceLineNo">033</span>    private final MessageDigest sha1;<a name="line.33"></a>
<span class="sourceLineNo">034</span><a name="line.34"></a>
<span class="sourceLineNo">035</span>    public DefaultStorageIdGenerator() {<a name="line.35"></a>
<span class="sourceLineNo">036</span>        try {<a name="line.36"></a>
<span class="sourceLineNo">037</span>            this.sha1 = MessageDigest.getInstance("SHA-1");<a name="line.37"></a>
<span class="sourceLineNo">038</span>        } catch (NoSuchAlgorithmException e) {<a name="line.38"></a>
<span class="sourceLineNo">039</span>            throw new RuntimeException(e);<a name="line.39"></a>
<span class="sourceLineNo">040</span>        }<a name="line.40"></a>
<span class="sourceLineNo">041</span>    }<a name="line.41"></a>
<span class="sourceLineNo">042</span><a name="line.42"></a>
<span class="sourceLineNo">043</span>    @Override<a name="line.43"></a>
<span class="sourceLineNo">044</span>    public int generateClassStorageId(Class&lt;?&gt; type, String name) {<a name="line.44"></a>
<span class="sourceLineNo">045</span>        return this.getStorageId("class:" + name);<a name="line.45"></a>
<span class="sourceLineNo">046</span>    }<a name="line.46"></a>
<span class="sourceLineNo">047</span><a name="line.47"></a>
<span class="sourceLineNo">048</span>    @Override<a name="line.48"></a>
<span class="sourceLineNo">049</span>    public int generateCompositeIndexStorageId(Class&lt;?&gt; type, String name, int[] fields) {<a name="line.49"></a>
<span class="sourceLineNo">050</span>        return this.getStorageId("index:" + name);<a name="line.50"></a>
<span class="sourceLineNo">051</span>    }<a name="line.51"></a>
<span class="sourceLineNo">052</span><a name="line.52"></a>
<span class="sourceLineNo">053</span>    @Override<a name="line.53"></a>
<span class="sourceLineNo">054</span>    public int generateFieldStorageId(Method getter, String name) {<a name="line.54"></a>
<span class="sourceLineNo">055</span>        return this.getStorageId("field:" + name);<a name="line.55"></a>
<span class="sourceLineNo">056</span>    }<a name="line.56"></a>
<span class="sourceLineNo">057</span><a name="line.57"></a>
<span class="sourceLineNo">058</span>    @Override<a name="line.58"></a>
<span class="sourceLineNo">059</span>    public int generateSetElementStorageId(Method getter, String name) {<a name="line.59"></a>
<span class="sourceLineNo">060</span>        return this.getStorageId("field:" + name + "." + SetField.ELEMENT_FIELD_NAME);<a name="line.60"></a>
<span class="sourceLineNo">061</span>    }<a name="line.61"></a>
<span class="sourceLineNo">062</span><a name="line.62"></a>
<span class="sourceLineNo">063</span>    @Override<a name="line.63"></a>
<span class="sourceLineNo">064</span>    public int generateListElementStorageId(Method getter, String name) {<a name="line.64"></a>
<span class="sourceLineNo">065</span>        return this.getStorageId("field:" + name + "." + ListField.ELEMENT_FIELD_NAME);<a name="line.65"></a>
<span class="sourceLineNo">066</span>    }<a name="line.66"></a>
<span class="sourceLineNo">067</span><a name="line.67"></a>
<span class="sourceLineNo">068</span>    @Override<a name="line.68"></a>
<span class="sourceLineNo">069</span>    public int generateMapKeyStorageId(Method getter, String name) {<a name="line.69"></a>
<span class="sourceLineNo">070</span>        return this.getStorageId("field:" + name + "." + MapField.KEY_FIELD_NAME);<a name="line.70"></a>
<span class="sourceLineNo">071</span>    }<a name="line.71"></a>
<span class="sourceLineNo">072</span><a name="line.72"></a>
<span class="sourceLineNo">073</span>    @Override<a name="line.73"></a>
<span class="sourceLineNo">074</span>    public int generateMapValueStorageId(Method getter, String name) {<a name="line.74"></a>
<span class="sourceLineNo">075</span>        return this.getStorageId("field:" + name + "." + MapField.VALUE_FIELD_NAME);<a name="line.75"></a>
<span class="sourceLineNo">076</span>    }<a name="line.76"></a>
<span class="sourceLineNo">077</span><a name="line.77"></a>
<span class="sourceLineNo">078</span>    private int getStorageId(String string) {<a name="line.78"></a>
<span class="sourceLineNo">079</span>        this.sha1.reset();<a name="line.79"></a>
<span class="sourceLineNo">080</span>        final byte[] digest = this.sha1.digest(string.getBytes(Charset.forName("UTF-8")));<a name="line.80"></a>
<span class="sourceLineNo">081</span>        int value = 0;<a name="line.81"></a>
<span class="sourceLineNo">082</span>        for (int i = 0; i &lt; 4; i++)<a name="line.82"></a>
<span class="sourceLineNo">083</span>            value = (value &lt;&lt; 8) | (digest[i] &amp; 0xff);<a name="line.83"></a>
<span class="sourceLineNo">084</span>        value &amp;= 0x7fffffff;<a name="line.84"></a>
<span class="sourceLineNo">085</span>        return (value % (MAX_STORAGE_ID - MIN_STORAGE_ID)) + MIN_STORAGE_ID;<a name="line.85"></a>
<span class="sourceLineNo">086</span>    }<a name="line.86"></a>
<span class="sourceLineNo">087</span>}<a name="line.87"></a>
<span class="sourceLineNo">088</span><a name="line.88"></a>




























































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